Transformer having improved heat dissipating system

ABSTRACT

Heat dissipation from an electrical transformer having a core and coil assembly immersed in oil within the transformer casing and a gas cushion above the oil is increased by a plurality of metallic fins attached to the inner surface of the metallic cover which depend through the gas cushion with their ends immersed in the oil and augment the amount of heat transmitted from the hot oil through the gas cushion to the cover.

United States Patent Hariow 51 Jan. 23, 1973 I 1 TRANSFORMER HAVINGIMPROVED 3,390,541 7/1968 Johnson eta] ..336/58 x HEAT DISSIPATINGSYSTEM 2,947,957 8/1960 Spindler 97 6 1751 inventor: James H. Harlow,Gadsden, Ala. 1 33 X [73] Assignee: Allis-Chalmers Corporation, Mil-Primary ExaminerThomas J. Kozma waukee, Wis. Attorney-Lee H. Kaiser etal.

[22] Filed: Aug. 12,1971

[57] ABSTRACT [21] Appl. No.1 171,296 I Heat dissipation from anelectrical transformer havmg a core and coil assembly immersed in oilwithin the [52] US. Cl ..336/58, 174/15 R, 336/61 transformer casing anda gas cushion above the oil is [51 Ilil. Cl ..H0lf 27/08 increased by aplurality of metallic fins attached to the Fleld of Search 61, R innerSurface of the metallic cover depend through the gas cushion with theirends immersed in [56] References cued the oil and augment the amount ofheat transmitted UNITED STATES PATENTS from the hot oil through the gascushion to the cover.

3,145,357 8/1964 Gettino et a] ..336/58 X i I 4 Claims, 2 DrawingFigures TRANSFORMER HAVING IMPROVED HEAT DISSIPATING SYSTEM Thisinvention relates to a cooling system and more particularly to a coolingsystem for heat generating apparatus such as an electrical transformerimmersed in an insulating and cooling dielectric liquid.

Efforts are continuously being made in the electrical industry to reducethe size of pad-mounted residential transformers since the mostaesthetic appearance for a transformer in a residential area is aminimum, or inconspicuous appearance. Reduction in the size and weightof the magnetic core, winding copper and insulating liquid of apad-mounted transformer for the purpose of making it more compactreduces its ability to absorb large quantities of heat without anappreciable temperature rise. Operation of a transformer at hightemperature overloads substantially reduces the life of the transformerby reducing the useful life and strength of the electrical insulation.Direct sunlight on a padmounted transformer may raise its peak top-oiltemperature 8to 10C and thus contribute to high temperature overloadsand make more difficult the problem of reducing transformer size withouta corresponding increase in top-oil temperature.

It is an object of the invention to provide a residential pad-mountedtransformer having improved means for dissipating the heat generated bythe transformer windings, thereby permitting the transformer to be mademore compact for a given temperature rise.

This and other objects and advantages of the invention will be morereadily apparent from consideration of the following detaileddescription when read in conjunction with the accompanying drawingwherein:

FIG. 1 is a perspective view of a pad-mounted transformer embodying theinvention with a portion of the casing wall broken away to illustratethe internal comstruction; and

FIG. 2 is a view taken along line lI-II of FIG. 1.

Referring to the drawing, a pad-mounted transformer supported on aconcrete pad 11 at ground level has a metal casing 12 defining an aircompartment 14 and a hollow oil compartment 15 closed by a metallic topwall, or cover 16 and containing an insulating and cooling liquid 17such as transformer oil. A transformer core and coil assembly immersedin the oil 17 typically includes a cylindrical transformer coil 18inductively linked by a pair of back-to-back closed magnetic cores 19.Electrical connections from the primary and secondary windings (notshown) of transformer coil 18 are completed through insulating bushings(not shown) which extend through a sidewall 20 of oil compartment 15into air compartment 14 which is closed by a hinged cover member 22.

The windings of coil 18 carry electrical current which generate heatthat is transferred to the oil 17 and raises the temperature of the oil17 above the ambient. Heat from the oil 17 is dissipated to theatmosphere through the walls of casing 12 defining oil compartment 15. Agas cushion 24, which may be air, exists above the oil 17 in compartment15 to permit the oil 17 to expand when heated. The hottest portion ofthe oil 17 is adjacent its top surface but, in absence of the presentinvention, only a relatively small amount of heat from the oil istransmitted through the gas cushion 24 to the top wall 16 of casing 12and then dissipated by cover 16 to the atmosphere. The thermalconductivity of the air in cushion 24 is relatively low, andconsequently only a small amount of heat is transmitted from the hot oil17 through gas cushion 24 to metallic top wall, or cover 16.

In accordance with the invention, a plurality of elongated fins 26constructed of metal such as steel or aluminum having relatively highthermal conductivity are affixed to the inner surface of top wall 16.The fins 26 may be of L-shaped cross section as illustrated in thedrawing or of channel configuration and may extend substantially theentire length of top wall 16 with the cross bar 27 affixed by suitablemeans such as welding to the top wall 16 and the legs 28 thereofdepending a sufficient distance through air cushion 24 so that they areimmersed in the hot oil 17. The relatively high thermal conductivityfins 26 conduct heat from the hot oil 17 to the top wall 16 and raisethe surface temperature of the top wall 16 so that a materially greateramount of heat is dissipated to the atmosphere.

In one embodiment wherein top wall 16 has an area of approximately 720square inches, it was found that the top wall 16 radiated heat at therate of approximately 0.15 watts/in. or 108 watts when no fins wereprovided and the top oil temperature was 50 above ambient. With eightsteel channel fins affixed to the inner surface of top wall 16, the topwall 16 radiated approximately 0.25 watts/inf, or watts. Further, whenthe fins 26 are of still higher conductivity material such as aluminum(which has a thermal conductivity more than three times higher than thatof steel), the efficiency of the top wall 16 for cooling the transformeris still further increased and the number of fins can be reducedproportionally.

While only asingle embodiment of the invention has been illustrated anddescribed, it should be understood that I do not intend to be limited tothe single embodiment for many modifications and variations thereof willbe obvious to those skilled in the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In an electrical transformer, the combination of: a hollow metalliccasing mounted on a the horizontal surface of a level concrete groundpad,

a non-volatile cooling and insulating liquid within said casing,

a transformer core and coil assembly immersed in said liquid within saidcasing,

a metallic cover closing said casing and being spaced from the topsurface of said liquid to provide a gas cushion within said casing abovesaid liquid and beneath said cover, and

at least one elongated, vertical heat transfer fin having a high thermalconductivity relative to the gas in said cushion affixed to andextending a substantial distance along the inner surface of said coverand depending through said gas cushion and having its end immersed insaid liquid, whereby heat is transmitted from said liquid through saidheat transfer member to said cover and the heat dissipation from the topsurface of said cover to the atmosphere is increased.

2. In an electrical transformer having a casing provided with acompartment containing a non-volatile cooling and insulating liquid,

a level concrete ground pad having a horizontal upper surface on whichsaid casing is mounted,

a transformer core and coil assembly immersed in said liquid within saidcompartment, a metallic cover closing said compartment and being spacedabove the top surface of said liquid, and a gas cushion within saidcompartment above the top surface of said liquid and below said cover,the improvement comprising a plurality of elongated, vertical heattransfer metallic fins affixed in spaced apart relation to and extendinga substantial distance along the inner surface of said cover anddepending through said gas cushion with their ends immersed in saidliquid, whereby heat is transmitted from said liquid through saidmetallic fins to said cover and the heat'dissipation from the topsurface of said cover to the atmosphere is increased.

3. In an electrical transformer in accordance with claim 2 wherein saidfins are elongated channels having the web thereof affixed to the innersurface of said cover and the legs thereof depending through said gascushion with the ends of said legs immersed in said liquid.

4. in a pad-mounted electrical transformer having a metallic casing withan oil compartment therein,

a level concrete ground pad having a horizontal upper surface on whichsaid casing is mounted,

transformer oil in said compartment,

a transformer core and coil assembly immersed in said oil,

a metallic cover closing said compartment and being spaced above the topsurface of said transformer oil,

a gas cushion within said compartment above said oil and beneath saidcover, and

a plurality of elongated vertical metallic heat transfer fins affixed inspaced apart relation to and extending a substantial distance along theundersurface of said cover and depending from said cover through saidgas cushion with their ends immersed in said liquid, whereby heat istransmitted from said transformer oil through said heat transfer fins tosaid cover and the heat dissipation from the top surface of said coverto the atmosphere is increased.

1. In an electrical transformer, the combination of: a hollow metalliccasing mounted on a the horizontal surface of a level concrete groundpad, a non-volatile cooling and insulating liquid within said casing, atransformer core and coil assembly immersed in said liquid within saidcasing, a metallic cover closing said casing and being spaced from thetop surface of said liquid to provide a gas cushion within said casingabove said liquid and beneath said cover, and at least one elongated,vertical heat transfer fin having a high thermal conductivity relativeto the gas in said cushion affixed to and extending a substantialdistance along the inner surface of said cover and depending throughsaid gas cushion and having its end immersed in said liquid, wherebyheat is transmitted from said liquid through said heat transfer memberto said cover and the heat dissipation from the top surface of saidcover to the atmosphere is increased.
 2. In an electrical transformerhaving a casing provided with a compartment containing a non-volatilecooling and insulating liquid, a level concrete ground pad having ahorizontal upper surface on which said casing is mounted, a transformercore and coil assembly immersed in said liquid within said compartment,a metallic cover closing said compartment and being spaced above the topsurface of said liquid, and a gas cushion within said compartment abovethe top surface of said liquid and below said cover, the improvementcomprising a plurality of elongated, vertical heat transfer metallIcfins affixed in spaced apart relation to and extending a substantialdistance along the inner surface of said cover and depending throughsaid gas cushion with their ends immersed in said liquid, whereby heatis transmitted from said liquid through said metallic fins to said coverand the heat dissipation from the top surface of said cover to theatmosphere is increased.
 3. In an electrical transformer in accordancewith claim 2 wherein said fins are elongated channels having the webthereof affixed to the inner surface of said cover and the legs thereofdepending through said gas cushion with the ends of said legs immersedin said liquid.
 4. In a pad-mounted electrical transformer having ametallic casing with an oil compartment therein, a level concrete groundpad having a horizontal upper surface on which said casing is mounted,transformer oil in said compartment, a transformer core and coilassembly immersed in said oil, a metallic cover closing said compartmentand being spaced above the top surface of said transformer oil, a gascushion within said compartment above said oil and beneath said cover,and a plurality of elongated vertical metallic heat transfer finsaffixed in spaced apart relation to and extending a substantial distancealong the undersurface of said cover and depending from said coverthrough said gas cushion with their ends immersed in said liquid,whereby heat is transmitted from said transformer oil through said heattransfer fins to said cover and the heat dissipation from the topsurface of said cover to the atmosphere is increased.